Biology subjects

Hahn, F.

Publications and source records attributed to Hahn, F..

8 recordsLinked to original sources

bioRxiv2026

Human cytomegalovirus antagonizes SMC5/6 driven genome silencing via UL35 instituted proteasomal degradation of SLF2

Recent studies demonstrated that the structural maintenance of chromosomes complex 5/6 (SMC5/6) acts as an important antiviral restriction factor that silences episomal DNA. Consequently, viruses have evolved strategies to antagonize this defence system. Interestingly, it was shown that SMC5/6-mediated silencing of extrachromosomal DNA depends on its recruitment to PML nuclear bodies which is mediated by a protein termed SMC5/6 localization factor 2 (SLF2). Since human cytomegalovirus (HCMV) dissociates PML nuclear bodies (PML-NBs) during the first hours of infection, we asked for the fate of SMC5/6 components during the HCMV replicative cycle. We first investigated the expression levels of SMC5/6 core components at the onset of HCMV infection and found that they were not downregulated by HCMV. Instead, we observed a distinct decrease of SLF2 protein levels which correlated with a complete dispersal of the SMC5/6 complex from PML-NBs. This was also observed after infection with UV inactivated HCMV and could not be blocked by cycloheximide treatment suggesting the involvement of an imported structural component of the virion. While we could exclude a role of the HCMV tegument protein pp71 (UL82), a targeted screen identified the tegument protein UL35 as being required and sufficient for proteasomal degradation of SLF2. In line with these results, SLF2 levels remained stable after infection with a recombinant HCMV harbouring a stop codon within the UL35 gene region and this correlated with a defect in the onset of HCMV immediate early gene expression. Furthermore, we observed an enhanced recruitment of SMC5/6 to PML-NBs and an overall increase in the association of parental viral genomes with SMC5/6 containing PML-NBs in the absence of UL35. Congruently, siRNA mediated depletion of SLF2 resulted in a reversal of this phenotype. This strongly suggests that UL35 serves as a novel viral SLF2 antagonist to prevent the initial silencing of incoming viral genomes by SMC5/6. Author summaryHuman cytomegalovirus (HCMV) is an important human pathogen which establishes a life-long persistent infection. Previous research revealed that host intrinsic defense mechanisms can silence HCMV gene expression and thereby foster latency. However, during lytic infection, viral effector proteins like the structural protein pp71 (UL82) and the viral immediate-early protein IE1 act as antagonists of this defense. Here, we report on the identification of a novel antagonist of host-mediated viral gene silencing which targets the SMC5/6 complex. SMC5/6 belongs to a highly conserved family of protein complexes that act as loop extrusion machines to facilitate the folding of chromatin. While SMC5/6 core factors were not attacked by HCMV, we found that the SMC5/6 associated protein SLF2 was degraded by the viral tegument protein UL35, that is imported into infected cells. This abrogates the accumulation of SMC5/6 at PML nuclear bodies which compromises the entrapment of viral genomes in these subnuclear structures. Since SLF2 is also important for genome stability and pathogenic variants of SLF2 cause the neurodevelopmental disease Atelis syndrome, we speculate that depletion of this factor via a viral tegument protein may also contribute to DNA damage induced during congenital HCMV infection.

microbiology↗

bioRxiv2025

Developing a Molecular Toolkit to ENABLE all to apply CRISPR/Cas9-based Gene Editing in planta

Gene editing, especially the CRISPR/Cas9 (Clustered Regulatory Interspaced Short Palindromic Repeats/CRISPR associated protein 9) system, has revolutionized trait development in crops. However, large parts of the world are missing out on applying CRISPR in planta. There is an obvious lack of gene editing applications in locally relevant crops in the Global South which tend to be neglected by mainstream agricultural research and development. Access barriers to these new breeding technologies need to be removed to allow the potential impact of these technologies on food security to happen. Here, we present the ENABLE(R) Gene Editing in planta toolkit, a minimal molecular toolbox allowing users to create a CRISPR knockout vector for transient or stable plant transformation in two simple cloning steps. We validate the toolkit in rice (Oryza sativa) protoplasts and in Arabidopsis thaliana plants. The ENABLE(R) kit is designed to be utilized specifically by users in the Global South who are new to CRISPR technology by providing a simple workflow, extensive accompanying protocols as well as options for low cost methods for cloning verification and gene editing verification in planta. We hope that our toolkit helps bridge the gap between the recent biotechnological advancements in plant breeding that high income countries can access and the lack of those technologies in low and middle income countries.

plant biology↗

bioRxiv2025

A correlative workflow streamlines synaptic imaging by cryo-electron tomography

Despite decades of intense research, the molecular organization of the synapse is not well understood. To address this issue, we sought to develop a method for systematic imaging of synapses by cryo-electron tomography (cryo-ET), a technology capable of mapping cellular architecture at molecular resolution. Thinning of cellular samples by cryo-focused ion beam milling is a prerequisite for high-quality cryo-ET imaging, but this process needs to be guided to the structures of interest. To allow robust synaptic targeting, we established a correlative cryo-light/electron microscopy approach by which synapses are fluorescently labeled in a minimally invasive manner, using a synthetic binder of the postsynaptic scaffold PSD-95 and antibodies against the presynaptic protein Synaptotagmin-1. Cryo-ET imaging at sites of colocalization consistently revealed excitatory synapses. Our method allows structural studies of synaptic protein complexes in situ, facilitating investigations of the molecular architecture of synapses.

neuroscience↗

bioRxiv2024

Realisation of a key step in the evolution of C4 photosynthesis in rice by genome editing.

C4 photosynthesis is a repeatedly evolved adaptation to photosynthesis that functions to reduce energy loss from photorespiration. The recurrent evolution of this adaptation is achieved through changes in the expression and localisation of several enzymes and transporters that are conventionally used in non-photosynthetic metabolism. These alterations result in the establishment of a biochemical CO2 pump that increases the concentration of CO2 around rubisco in a cellular environment where rubisco is protected from oxygen thus preventing the occurrence of photorespiration. A key step in the evolution of C4 photosynthesis is the change in subcellular localisation of carbonic anhydrase (CA) activity from the mesophyll cell chloroplast to the cytosol, where it catalyzes the first biochemical step of the C4 pathway. Here, we achieve this key step in C4 evolution in the C3 plant Oryza sativa (rice) using genome editing. We show that editing the chloroplast transit peptide of the primary CA isoform in the leaf results in relocalisation of leaf CA activity from the chloroplast to the cytosol. Through analysis of fluorescence induction kinetics in these CA relocalisation lines we uncover a role a new role for chloroplast CA in photosynthetic induction. We also reveal that relocalisation of CA activity to the cytosol causes no detectable perturbation to plant growth or leaf-level CO2 assimilation. Collectively, this work uncovers a novel role for chloroplast CA in C3 plants, and demonstrates that it is possible to achieve a key step in the evolution of C4 photosynthesis by genome editing. Significance statementC4 photosynthesis is a highly efficient adaptation to photosynthesis that fuels the worlds most productive crop plants. It evolved from conventional C3 photosynthesis through a series of changes in leaf biochemistry and anatomy. Here we achieve a key evolutionary step on the path to C4 photosynthesis in rice using genome editing. Specifically, we alter the primary location of carbonic anhydrase activity in the rice leaf from the chloroplast to the cytosol. In doing so, we uncover a novel role for carbonic anhydrase in facilitating the rapid induction kinetics of photosystem II, and initiate a new era of C4 engineering using precision breeding techniques.

plant biology↗

bioRxiv2021

Efficient CRISPR/Cas-mediated Targeted Mutagenesis in Spring and Winter Wheat Varieties

The CRISPR/Cas technology has recently become a molecular tool of choice for gene function studies in plants as well as crop improvement. Wheat is a globally important staple crop with a well annotated genome and there is plenty of scope for improving its agriculturally important traits using genome editing technologies, such as CRISPR/Cas. As part of this study we targeted three different genes in hexaploid wheat Triticum aestivum: TaBAK1-2 in the spring cultivar Cadenza as well as Ta-eIF4E and Ta-eIF(iso)4E in winter cultivars Cezanne, Goncourt and Prevert. The primary transgenic lines carrying CRISPR/Cas-induced indels were successfully generated for all targeted genes. As winter wheat varieties are generally less amenable to genetic transformation, the successful experimental methodology for transformation and genome editing in winter wheat presented in this study will be of interest to the research community working with this crop.

plant biology↗

bioRxiv2020

Remarkable recent changes in genetic diversity of the avirulence gene AvrStb6 in global populations of the wheat pathogen Zymoseptoria tritici

Septoria tritici blotch (STB), caused by the fungus Zymoseptoria tritici, is one of the most economically important diseases of wheat. Recently, both factors of a gene-for-gene interaction between Z. tritici and wheat, the wheat receptor-like kinase Stb6 and the Z. tritici secreted effector protein AvrStb6, have been identified. Previous analyses revealed a high diversity of AvrStb6 alleles present in historic Z. tritici isolate collections, with up to ~ 18% of analysed isolates possessing the avirulence isoform of AvrStb6 identical to that originally identified in the reference isolate IPO323. With Stb6 present in many commercial wheat cultivars globally, we aimed to assess potential changes in AvrStb6 genetic diversity and the incidence of alleles allowing evasion of Stb6-mediated resistance in more recent Z. tritici populations. Here we show, using targeted re-sequencing of AvrStb6, that this gene is universally present in field isolates sampled from major wheat-growing regions of the world between 2013-2017. However, in contrast to the data from studies of historic isolates, our study revealed a complete absence of the originally described avirulence isoform of AvrStb6 amongst modern Z. tritici isolates. Moreover, a remarkably small number of alleles, each encoding AvrStb6 protein isoforms conditioning virulence on Stb6-containing wheat, were found to predominate among modern Z. tritici isolates. A single virulence isoform of AvrStb6 was found to be particularly abundant throughout the global population. These findings indicate that, despite the ability of Z. tritici to sexually reproduce on resistant hosts, AvrStb6 avirulence alleles tend to be eliminated in subsequent populations.

microbiology↗

bioRxiv2019

A modular cloning toolkit for genome editing in plants

BackgroundCRISPR/Cas has recently become a widely used genome editing tool in various organisms, including plants. Applying CRISPR/Cas often requires delivering multiple expression units into plant and hence there is a need for a quick and easy cloning procedure. The modular cloning (MoClo), based on the Golden Gate (GG) method, has enabled development of cloning systems with standardised genetic parts, e.g. promoters, coding sequences or terminators, that can be easily interchanged and assembled into expression units, which in their own turn can be further assembled into higher order multigene constructs.\n\nResultsHere we present an expanded cloning toolkit that contains ninety-nine modules encoding a variety of CRISPR/Cas-based nucleases and their corresponding guide RNA backbones. Among other components, the toolkit includes a number of promoters that allow expression of CRISPR/Cas nucleases (or any other coding sequences) and their guide RNAs in monocots and dicots. As part of the toolkit, we present a set of modules that enable quick and facile assembly of tRNA-sgRNA polycistronic units without a PCR step involved. We also demonstrate that our tRNA-sgRNA system is functional in wheat protoplasts.\n\nConclusionsWe believe the presented CRISPR/Cas toolkit is a great resource that will contribute towards wider adoption of the CRISPR/Cas genome editing technology and modular cloning by researchers across the plant science community.

plant biology↗

bioRxiv2018

Homology-directed repair of a defective glabrous gene in Arabidopsis with Cas9-based gene targeting

The CRISPR/Cas9 system has emerged as a powerful tool for targeted genome editing in plants and beyond. Double-strand breaks induced by the Cas9 enzyme are repaired by the cells own repair machinery either by the non-homologous end joining pathway or by homologous recombination. While the first repair mechanism results in random mutations at the double-strand break site, homologous recombination uses the genetic information from a highly homologous repair template as blueprint for repair of the break. By offering an artificial repair template, this pathway can be exploited to introduce specific changes at a site of choice in the genome. However, frequencies of double-strand break repair by homologous recombination are very low. In this study, we compared two methods that have been reported to enhance frequencies of homologous recombination in plants. The first method boosts the repair template availability through the formation of viral replicons, the second method makes use of an in planta gene targeting approach. Additionally, we comparatively applied a nickase instead of a nuclease for target strand priming. To allow easy, visual detection of homologous recombination events, we aimed at restoring trichome formation in a glabrous Arabidopsis mutant by repairing a defective glabrous1 gene. Using this efficient visual marker, we were able to regenerate plants repaired by homologous recombination at frequencies of 0.12% using the in planta gene targeting approach, while both approaches using viral replicons did not yield any trichome-bearing plants.

plant biology↗